Jan Ribbe, Amy E. Baker, Sebstian Euler, George A. O'Toole and Berenike Maier
For Pseudomonas aeruginosa the levels of cyclic di-GMP govern the transition from the planktonic state to biofilm formation. Type IV pili (T4P) are crucial determinants of biofilm structure and dynamics, but it is unknown how the levels of c-di-GMP affect pilus dynamics. Here, we scrutinized how c-di-GMP affects molecular motor properties and adhesive behavior of T4P. By means of retraction, T4P generated forces of ∼ 30 pN. Deletion mutants in the proteins with known roles in biofilm formation, swarming motility and exopolysaccharide (EPS) production, specifically, the diguanulate cyclases sadC and roeA or the c-di-GMP phosphodiesterase bifA, showed only modest effects on velocity or force of T4P retraction. At high levels of c-di-GMP, the production of exopolysaccharides (EPS) and in particular of Pel is upregulated. We found that Pel production strongly enhances T4P-mediated surface adhesion of P. aeruginosa, suggesting that that T4P — matrix interactions may be involved in biofilm formation by P. aeruginosa. Finally, our data are consistent with the previously proposed sling-shot-like “twitching” motility of P. aeruginosa.